Nov 26, 2008

Science - Deep sleep ups creativity,memory

WASHINGTON: Just in time for the holidays, some medical advice most people will like: Take a nap. Interrupting sleep seriously disrupts memory-making, compelling new research suggests. But on the flip side, taking a nap may boost a sophisticated kind of memory that helps us see the big picture and get creative.

"Not only do we need to remember to sleep, but most certainly we sleep to remember," is how William Fishbein, a cognitive neuroscientist at the City University of New York, put it at a meeting of the Society for Neuroscience last week. Scientists increasingly are focusing less on sleep duration and more on the quality of sleep, what's called sleep intensity, in studying how sleep helps the brain process memories so they stick. Particularly important is "slow-wave sleep", a period of very deep sleep that comes earlier than better-known REM sleep, or dreaming time.

Fishbein suspected a more active role for the slow-wave sleep that can emerge even in a power nap. Maybe our brains keep working during that time to solve problems and come up with new ideas.

He taught 20 English-speaking college students lists of Chinese words spelled with two characters — such as sister, mother, maid. Then half the students took a nap, being monitored to be sure they didn't move from slow-wave sleep into the REM stage.

Upon awakening, they took a multiple-choice test of Chinese words they'd never seen before. The nappers did much better at automatically learning that the first of the two-pair characters in the words they'd memorized earlier always meant the same thing — female, for example. So they also were more likely than non-nappers to choose that a new word containing that character meant "princess" and not "ape".

Conversely, Wisconsin researchers briefly interrupted nighttime slow-wave sleep by playing a beep — just loudly enough to disturb sleep but not awaken — and found those people couldn't remember a task they'd learned the day before as well as people whose slow-wave sleep wasn't disrupted.

That brings us back to fragmented sleep, whether from aging or apnea. It can suppress cell birth in the hippocampus, where memory-making starts — enough to hinder learning weeks after sleep returns to normal, warns Dennis McGinty of the University of California, Los Angeles.

McGinty found that rats with disturbed sleep could only randomly stumble upon an escape hole in a maze that their counterparts detected easily by using room cues.